An active matrix substrate for use in a liquid crystal display device or the like includes a switching element for each pixel, e.g., a thin film transistor (hereinafter, “TFT”). As such switching elements, TFTs whose active layer is an amorphous silicon film (hereinafter, “amorphous silicon TFT”, and TFTs whose active layer is a polycrystalline silicon film (hereinafter “polycrystalline silicon TFT”), have been widely used.
In recent years, it has been proposed to use an oxide semiconductor as the material of an active layer of a TFT, instead of an amorphous silicon or a polycrystalline silicon. A TFT having an oxide semiconductor film as an active layer is referred to as an “oxide semiconductor TFT”. Patent Document 1 discloses an active matrix substrate in which an In—Ga—Zn—O based semiconductor film is used as active layers of TFTs.
An oxide semiconductor provides a higher mobility than does an amorphous silicon. Therefore, oxide semiconductor TFTs can operate more rapidly than amorphous silicon TFTs. Moreover, an oxide semiconductor film is formed through a simple process as compared to a polycrystalline silicon film, and therefore is applicable to devices which require a large geometric area.
Generally speaking, an active matrix substrate includes an active region and a peripheral region. The active region includes a plurality of pixels, and is also called a display region. The peripheral region, which is located around the active region, is also called a frame region.
Provided in the active region are: TFTs which are formed correspondingly for the respective pixels; and gate lines, source lines, and pixel electrodes which are electrically connected respectively to the gate electrodes, source electrodes, and drain electrodes of the TFTs. The TFTs are covered by an interlevel dielectric layer, with the pixel electrodes being formed on the interlevel dielectric layer. A construction for the interlevel dielectric layer is known in which an inorganic dielectric layer (passivation film) that is made of an inorganic insulative material and an organic dielectric layer (planarization film) that is made of an organic insulative material are stacked.
In the peripheral region, a plurality of terminal portions are provided for allowing the gate lines and source lines to be electrically connected to external wiring lines. For example, a gate line may extend from the active region to the peripheral region, where it may be connected to a gate driver via a terminal portion (gate terminal portion). On the other hand, a source line may be electrically connected to a gate connection line that is made of the same conductive film as the gate lines, for example. A gate connection line may be connected to a source driver via a terminal portion (source terminal portion) in the peripheral region.